You might've left an app running? If not maybe there's a battery issue.
If I charge my ipad overnight and unplug it in the morning, its always still at 100% 8 hours later
Please clarify - are you saying that in the morning your iPad states a 100% charge, then you go to work (and assuming no one is using the iPad when you are at work?), you return from work and your battery now indicates a 90% or so charge - is this your correct question?
My first suggestion is to check to see if you may have 'open' apps that could be using power - the apps 'in suspension' in your taskbar are not likely consuming this amount of power; also, are you leaving your Wi-Fi & Bluetooth transmitters on? If the latter is true, you may want to turn those radios off one morning and then recheck your battery's reserve at night - just an initial suggestion - good luck!
The culprit is likely Notifications. It doesn't use a lot of power, but there is some usage involved in activating the screen, playing the sound, etc. You could also be doing automated downloads when away.
Another typical culprit is folks setting "email fetch" to a regular schedule. If you want to minimise your battery usage when the iPad is idle, consider setting email fetch to "manually". That way, emails will only be retrieved from your "fetch" accounts when you open the email app. This does not effect "push" accounts.